It is well known that endurance exercise training (Tr) renders the heart more resistant to ischemia and reperfusion injury. To date, the cellular basis for these adaptations has not been clearly identified. In the heart, ATP-sensitive K channels exist on the sarcolemma (sI-KATP) and in mitochondria (mito-KATP) and both have been implicated in protecting the heart against ischemic injury. We recently found that Tr elicits a marked reduction in the magnitude of an anoxia-inducible, glibenclamide-sensitive outward K current (IK,ATP) in single rat ventricular cardiocytes. In Specific Aim 1, we will use electrophysiological (whole cell and excised patch) and immunoblotting techniques to determine the cellular basis for this finding. We will examine the effect of training on (1) the sensitivity of sI-KATP to inhibition by ATP and ADP, (2) the protein expression of sI-KATP channel subunits (Kit6.2 and SUR2A), and (3) mitochondrial ATP production in the face of ischemic stress. We also found that following severe zonal ischemia elicited by coronary artery occlusion and then reperfusion, Tr produced infarct sparing and augmented mechanical function in isolated perfused hearts. We also observed a marked Tr-induced hyperemia that was apparent throughout the ischemia reperfusion protocol. In Specific Aim 2, we will use KATP antagonists that are selective for sl- and mito-KATP channels to identify the involvement of these specific channels in Tr-induced infarct sparing and preservation of mechanical function. Indomethacin and L-NAME will be used in studies to determine the cellular basis for the hyperemia that was exhibited during post-ischemic reperfusion, and the extent to which the Tr-induced hyperemia contributed to infarct sparing and the preservation of mechanical function in the heart. The experiments in Aim 2 include a comprehensive battery of LV function, metabolite, biochemical, and coronary flow measurements. Exercise training is known to be effective in the prevention and treatment of a wide variety of cardiopathologic conditions. Elucidation of the cellular changes that underlie these positive adaptations may be of particular importance in the design, development, and implementation of molecular and pharmacological heart disease treatment and prevention strategies. This is particularly significant in view of the fact that heart disease claims more North American lives than any other disease.